Colloidal silica for semiconductor wafer polishing and production method thereof

ABSTRACT

Colloidal silica forming nonspherical particles cluster, whose long axis/short axis ratio of silica particles is of 1.2 to 20, and average long axis/short axis ratio of 3 to 15. This colloidal silica can be produced by forming particles by adding basic nitrogen compounds to an active silicic acid aqueous solution, the solution which produced by hydrolysis of tetraalkoxysilane, while heating, then growing particles by using a build up method.

FIELD OF THE INVENTION

The present invention relates to colloidal silica for semiconductorwafer polishing that polishes a surface or an edge part of asemiconductor wafer such as a silicon wafer or a semiconductor devicesubstrate with a film such as a metal film, an oxide film, a nitridefilm or the like (hereinafter shortened to metal films) on the surface,and the production method thereof.

Hereinafter, “colloidal silica for semiconductor wafer polishing” can beshortened to “colloidal silica for polishing”.

BACKGROUND OF THE INVENTION

Electronic components such as ICs, LSIs or ULSIs which applyingsemiconductor materials, such as silicon single crystal, as raw materialcan be manufactured based on a small semiconductor device chips. Saidsmall semiconductor device chips are fabricated by dicing thin diskshaped wafers on which a number of fine electronic circuits are built tosemiconductor chips, where the wafers are fabricated by slicing a singlecrystal ingot of silicon or semiconductors of other compound to thindisk shaped wafers. A wafer sliced from the ingot is processed into amirror wafer with a mirror finished surface and edge through theprocesses of lapping, etching, and polishing. In following devicemanufacturing process, fine electric circuits are formed on the mirrorfinished surface of the wafer. At present, from the view point ofdeveloping high speed LSIs, material for wiring has changed fromconventional Al to Cu, which is characterized to have lower electricresistance. Also an insulation film existing between wirings has changedfrom a silicon oxidation film to a low permittivity film which ischaracterized to have lower permittivity. Further, for the purpose ofprotecting the diffusion of Cu into the low permittivity film, a wiringforming process is shifting to a new process which interposing a barrierfilm made from tantalum or tantalum nitride between Cu and the lowpermittivity film. According to such a circuit structure formation and ahigh integration requirement, a polishing process is carried outfrequently and repeatedly to planarize the interlayer insulation film,to form a metal plug between upper and lower wirings, to form anembedded wiring or the like. Generally, the polishing step is processedby rotating the semiconductor wafer which is placed on and pressedagainst a platen on which a polishing cloth made from synthetic resinfoam, suede-like synthetic leather or the like is applied, while aquantitative amount of polishing compound solution is supplied so as topolish the semiconductor wafer.

On the edge surface of the wafer, above mentioned metal films or thelike are disorderly accumulated. Before dicing the wafer tosemiconductor device chips, various wafer transportation processesexist. The wafer is supported at the edge when it is subject to thetransportation and the like while keeping an initial disk shape. Ifoutermost periphery edge of the wafer is unevenly structured at thetransportation, minute crushes are caused at the edge part of the waferwhen the wafer collides with a transporting device and fine particlesarose. The fine particles arisen scatter and contaminate the preciselyprocessed wafer surface, and affect seriously on yield and quality ofproducts. To prevent the contamination by the fine particles, the edgepart of the semiconductor wafer is required to have a mirror polishingprocess after the metal films or the other are formed.

Above mentioned edge polishing is performed by a method mentioned below.First, an edge part of a semiconductor wafer is pressed against apolishing machine which has a polishing cloth supporter, on which apolishing cloth made from synthetic resin foam, synthetic leather,nonwoven fabric or the like is applied. Then, the polishing clothsupporter and/or the wafer are rotated while a polishing compoundsolution which containing polishing particles, such as silica, as a maincomponent is supplied. As the polishing particles to be contained insaid polishing compound, one can use colloidal silica which is similarto the one used for edge polishing of a silicon wafer, fumed silica,cerium oxide or alumina that is used for surface polishing of a devicewafer, or the like. Especially, colloidal silica and fumed silica claimattention because both silica are fine particles and smooth mirrorsurface can be easily obtained.

The polishing compound mentioned above is also called as “slurry”, whichmay be called as such in some cases below.

In general, a polishing compound which containing silica particles asmain components is given as a solution that contains alkalinecomponents. The polishing mechanism can be described as a combination ofa chemical action by the alkaline components, specifically, chemicalcorrosion of a surface of silicon oxide films, metal films, and the likeby the alkaline components, and a mechanical polishing action by silicaparticles. More specifically, by the corrosive action by the alkalinecomponents, thin and soft eroded layer is formed on a surface of anobject to be polished such as a wafer. Said eroded layer is removed bythe mechanical polishing action by fine polishing particles. Byrepeating said actions, the polishing process is progressed.

Further, device wiring is becoming remarkably finer and more preciseyear by year. According to “International Technology Roadmap forSemiconductors”, target width of device wiring is 50 nm in 2010 and 35nm in 2013. Considering finer tendency of width of device wiring, copperor copper alloy has become in use as a wiring material. As a polishingcompound to be used for semiconductor polishing, oxidative components ofcopper or selective etching components other than alkaline componentsare recommended. Especially, amines claim attention as an agent thatseldom over etches a wafer, however, a problem has not been solved.Since over etching of device wiring on the semiconductor wafer surfaceinhibits an operation of a device, it is a serious problem.

Up to the present, various polishing compounds have been proposed formirror polishing of semiconductor wafers. In Patent Document 1, apolishing compound prepared by dispersing silica in ethylenediamine orhydrazine is disclosed. According to the document, said polishingcompound can polish polysilicon at high speed while it seldom etches asilicon oxide insulation film, and providing an advantage that one canuse the insulation film as a stopper. In Patent Document 2, a polishingcompound prepared by dispersing polishing particles in an imidazoleaqueous solution or a methylimidazole aqueous solution is disclosed.According to the document, said polishing compound forms a coppercomplex which is water soluble and never produces water insoluble solidmatter other then polishing particles. Therefore, said polishingcompound can prevent scratches and can also prevent dishing because itcontrols etching of a copper oxide layer. In Patent Document 3, apolishing compound prepared by adding diethylenediamine or piperidine tocolloidal silica is disclosed. Said amines act as a weak base componentaiming to form a pH buffer solution. In Patent Document 4, a polishingcompound containing amino acid which possessing 2 or more nitrogen atomsin a molecular structure, such as arginine, is disclosed. According tothe document, said polishing compound has high polishing rate against acopper film, while has low polishing rate against a compound containingtantalum, and is characterized to have excellent selection ratio.

As disclosed in above mentioned Patent Documents 1 to 4,ethylenediamine, diethylenediamine, imidazole, methylimidazole,piperidine, arginine, and hydrazine are useful agents among basicnitrogen compounds for metal polishing. Regarding morpholine, adequatePatent Document can not be found out. Diethylenediamine is also calledas piperazine.

Further, many types of colloidal silica composed of nonspherical silicaparticles are proposed. In Patent Document 5, a stable silica sol whichprepared by dispersing amorphous colloidal silica particles into aliquid solvent is disclosed. Said amorphous colloidal silica particlesare elongated shaped silica that have uniformed thickness of 5 to 40 nmby an electron microscope observation and extend only in twodimensional. In Patent Document 6, a silica sol composed of amorphousand elongated colloidal silica particles is disclosed. Said silica solis prepared by growing metal compounds such as aluminum salt before, inthe middle or after an adding process of silica. In Patent Document 7, acolloidal silica composed of cocoon shaped silica particles whose longaxis/short axis ratio is in range of 1.4 to 2.2 and which produced byhydrolysis of alkoxysilane is disclosed. In Patent Document 8, aproduction method of colloidal silica containing nonspherical silicaparticles by using a hydrolysis solution of alkoxysilane instead of anactive silicic acid aqueous solution of water glass method andtetraalkylammonium hydroxide as an alkali agent is disclosed.

In a production process of colloidal silica mentioned in Patent Document5, there is an adding process of water soluble calcium salt, magnesiumsalt or mixture of salts, which is contained in a product as impurities.In a production process of colloidal silica mentioned in Patent Document6, there is an adding process of water soluble aluminum salts, which iscontained in a product as impurities. Colloidal silica mentioned inPatent Document 7 is desirable because of its high purity according tothe fact that using alkoxysilane as a silica source. However, ammoniaand large amount of alcohol are required in a reaction system whicharises disadvantages such as difficulty in removal of the components,price, and so on. Similarly, since colloidal silica mentioned in PatentDocument 8 also uses alkoxysilane as a silica source, it is also high inpurity and is desirable. One can produce said silica particles withnonspherical shape, however, technical investigation about adjustment ofparticle shape is not sufficient.

Patent Document 1: JPH2-146732 A publication

Patent Document 2: JP2005-129822 A publication

Patent Document 3: JPH11-302635 A publication

Patent Document 4: JP2002-170790 A publication

Patent Document 5: JPH1-317115 A publication (especially in claims)

Patent Document 6: JPH4-187512 A publication

Patent Document 7: JPH11-60232 A publication (especially in claims

Patent Document 8: JP2001-48520 A publication (especially in claims andin Examples)

DISCLOSURE OF THE INVENTION

The present invention relates to a colloidal silica for mirror polishingof a surface or an edge part of a semiconductor wafer, which preventsover etching of the semiconductor wafer surface while maintaining highpolishing rate and providing satisfactory surface roughness, and theproduction method thereof.

The inventors of the present invention have found that one can polish asurface or an edge part of a semiconductor wafer effectively by usingcolloidal silica which produced from an active silicic acid aqueoussolution obtained by hydrolysis of tetraalkoxysilane and specific basicnitrogen compounds, and accomplished present invention.

The first invention of the present invention is a colloidal silica forsemiconductor wafer polishing prepared from an active silicic acidaqueous solution obtained by hydrolysis of tetraalkoxysilane such astetramethoxysilane or tetraethoxysilane and specific basic nitrogencompounds, wherein said colloidal silica contains nonspherical silicaparticles. As basic nitrogen compounds, at least one compound selectedfrom the group consisting of ethylenediamine, diethylenediamine,imidazole, methylimidazole, piperidine, morpholine, arginine orhydrazine can be used. Further, it is desirable that quaternary ammoniumhydroxide, such as tetramethylammonium hydroxide, tetraethylammoniumhydroxide or choline (also known as trimethyl-2-hydroxyethylammoniumhydroxide) is contained. Also, it is desirable that the concentration ofalkali metal to entire solution of colloidal silica is less than 1 ppm.Furthermore, it is desirable to contain above mentioned components, andhas a pH of 8.5 to 11.0 at 25° C. Said colloidal silica is desirable toform a buffer solution by mixing basic nitrogen compounds and strongacid or by mixing weak acid and quaternary ammonium hydroxide, whichdisplays pH buffering action in the pH range of 8.5 to 11.0 at 25° C.

Nonspherical silica particles contained in said colloidal silica forpolishing is desirable to be nonspherical silica particles cluster whichhave long axis/short axis ratio of 1.2 to 20, average long axis/shortaxis ratio of 3 to 15, and average short axis length of 5 to 30 nm by atransmission electron microscope observation. Said colloidal silica forsemiconductor wafer polishing is desirable to be water dispersion whoseconcentration of silica to entire colloidal solution is of 2 to 50 wt %.

The second invention of the present invention is a production method ofcolloidal silica for semiconductor polishing comprising:

(a) a producing process of an active silicic acid aqueous solution byhydrolysis of tetraalkoxysilane with acid catalyst in a composition of 1to 8 mol/L tetrametoxysilane, 0.0018 to 0.18 mol/L acid, and 2 to 30mol/L water without using organic solvent, diluting with water so as toadjust the concentration within range of 0.2 to 1.5 mol/L; and

(b-1) a formation process of colloidal particles by heating said activesilicic acid aqueous solution after alkalizing the solution by addingsaid basic nitrogen compounds; and

(b-2) a growing process of colloidal particles by adding said activesilicic acid aqueous solution and an alkalizing agent or said activesilicic acid aqueous solution, said basic nitrogen compounds, and thealkalizing agent to colloidal particles formed in the process (b-1)while maintaining in alkaline condition under heating condition.

Having a process (c) a concentration process of the colloidal silicaafter the process (b-2) is desirable.

EFFECT OF THE INVENTION

By using a colloidal silica for polishing of the present invention, onecan obtain excellent effect in preventing over etching in polishing of asemiconductor wafer and the like. “Over etching” is a phenomenon thatcauses by corrosion of a wiring metal which results formation ofrecesses during polishing process of the wiring metal, an insulationfilm or a barrier film. Over etching occurs when a balance of corrosivespeed between a mechanical polishing action by polishing particles and acorrosive action by alkaline component is broken. Over etching isrecognized as a ground of defective products such as corrosive pits,wiring corrosions or key holes of tungsten wiring. Further, since saidcolloidal silica does not contain alkali metals, problems such asremaining of polishing particles or dispersion of alkali metal to wiringlayer can be prevented. By the present invention, the colloidal silicafor polishing with excellent polishing ability and continuance abilityfor mirror polishing which improve the flatness of the surface of thepolished wafer can be obtained, and the present invention has greatinfluence to the relating field.

BRIEF ILLUSTRATION OF DRAWINGS

FIG. 1: TEM picture of colloidal silica obtained in Example 1.

FIG. 2: TEM picture of colloidal silica obtained in Example 2.

FIG. 3: TEM picture of colloidal silica obtained in Example 5.

FIG. 4: TEM picture of colloidal silica obtained in Example 6.

DESCRIPTION OF PREFERRED EMBODIMENT

As mentioned above, basic nitrogen compounds are the useful agents inmetal polishing and are disclosed in many Patent Documents. In themeanwhile, a technique to obtain nonspherical silica particles using anactive silicic acid aqueous solution obtained by hydrolysis oftetraalkoxysilane is disclosed in Patent Document 8 and is the publicknown technique. However, a technique to obtain nonspherical silicaparticles by hydrolysis of tetraalkoxysilane using specific basicnitrogen compounds, such as ethylenediamine, diethylenediamine,imidazole, methylimidazole, piperidine, morpholine, arginine orhydrazine, is the first clarified technique by the present invention.

Ethylenediamine is a strong base whose logarithms of reciprocal numberof acid dissociation constant (pKa) is about 9.9 and a pH of a 1%aqueous solution is about 11.8. There are two sorts of ethylenediamine:ethylenediamine anhydride and ethylenediamine mono hydrate.Ethylenediamine mono hydrate is preferred because it is less dangerousagent. Another name of diethylenediamine is piperazine and is also knownas hexahydropyrazine or diethyleneimine. There are two sorts ofdiethylenediamine: diethylenediamine anhydride and diethylenediaminehexahydrate. Diethylenediamine hexahydrate is easier to use.Diethylenediamine is a strong base whose pKa is about 9.8 and a pH of a1% aqueous solution is about 11.5. Imidazole is a weak base whose pKa isabout 6.9 and a pH of a 1% aqueous solution is about 10.2.2-methylimidazole is a weak base whose pKa is about 7.8 and a pH of a 1%aqueous solution is about 10.7. 4-methylimidazole can also be usedinstead of 2-methylimidazole. Other names of piperidine arehexahydropyridine and pentamethyleneimine. Piperidine is a strong alkaliwhose pKa is about 11.1 and a pH of a 1% aqueous solution is about 12.3.Morpholine is a slightly weak base whose pKa is about 8.4 and a pH of a1% aqueous solution is about 10.8. Arginine is one of amino acids whichalso known as 5-guadidino-2-amino pentanoic acid and is a base whose pKais about 12.5 and a pH of a 1% aqueous solution is about 10.5 because itpossesses a carboxy group. Although each of D-, L- or DL-arginine can beused, L-arginine is preferably used among three because of low price.There are two sorts of hydrazine: hydrazine anhydrous and hydrazinemonohydrate (also known as hydrohydrazine or hydrazine hydrate).Hydrazine monohydrate is preferred because it is less dangerous agent.Hydrazine is a strong reducing agent, however, as a base, it is a weakbase whose pKa is about 8.1 and a pH of a 1% aqueous solution is about9.9.

It is desirable that any kind of above mentioned basic nitrogencompounds do not contain alkali metals. Since any kind of said basicnitrogen compounds except arginine has strong irritative feature,toxicity, and corrosive feature, it is desirable to be used as anaqueous solution of about 10% concentration.

Above mentioned basic nitrogen compounds act as a polymerizationcatalyst of silica of an active silicic acid aqueous solution due to itsbasic feature. That is, colloidal particles can be obtained by heatingthe active silicic acid aqueous solution after alkalizing the solutionby adding said basic nitrogen compounds. In the meanwhile said basicnitrogen compounds affect particle form at a growing process ofcolloidal particles. Said basic nitrogen compounds bond with or adsorbsto surfaces of silica particles in the growing process and inhibitsgrowing of particles at bonded parts and disturbs spherical growing ofparticles.

In the present invention, for the purpose of maintaining a stablepolishing ability at actual polishing processes, it is desirable tomaintain a solution at a pH of 8.5 to 12.5 at 25° C. When the pH islower than 8.5, polishing speed becomes slow and is out of practicaluse. Further, when the pH is higher than 11.0, the solution over etchesnonpolishing parts of a wafer and deteriorates a flatness of the waferand is again out of practical use.

Further, it is desirable that a pH of the solution does not changeeasily by exterior conditions such as abrasion, heating, contacting withouter atmosphere, mixing with other components or the like. Especially,in a case of edge polishing, a polishing compound is used by acirculation flow. That is, the polishing compound supplied from a slurrytank to polishing parts sent back to the slurry tank so that to bereused. In a case of a polishing compound that contains an alkalizingagent alone, a pH of the solution falls in short time since the solutionis diluted with pure water used in the circulation flow. The phenomenonis caused by influx of pure water, which is used as cleaning water.Alternation of the pH affects a polishing rate, and lack of polishing orover polishing is easily caused.

For the purpose of maintaining a pH of colloidal silica for polishing ofthe present invention, it is desirable that colloidal silica has abuffer function in a pH range of 8.5 to 11.0. Therefore, in the presentinvention, it is desirable to make colloidal silica for polishing itselfa strong buffer solution that does not change a pH dramaticallyaccording to exterior conditions. To form a buffer solution, a method ofblending basic nitrogen compounds in excess, followed by neutralizationof the excess part by adding strong acid to adjust pH value close to pKavalue of the basic nitrogen compounds can be mentioned. For example,when a pH of a solution is adjusted to 10.2 by adding hydrochloric acidto 1% diethylenediamine aqueous solution whose pH is about 11.5, the pHof the solution becomes stable against dilution or mixing with salts.That is, even if the solution has done the 1 to 10 dilution with purewater, the pH only changes to 10.1, resulting pH does not changedramatically by dilution or mixing with salts. Accordingly, it ispossible to adjust a pH at higher value compare to an aimed value andreduce the pH to the aimed value by adding strong acid. Further, asanother method, a method of adding a buffer solution prepared by mixingweak acid and strong base can be mentioned. For example, a method ofneutralizing a 25% tetramethylammonium hydroxide aqueous solution withcarbon dioxide gas to adjust a pH of 10.3, followed by addition of saidcarbonated tetramethylammonium hydroxide aqueous solution to colloidalsilica can be mentioned.

As a production method of an active silicic acid aqueous solution to beused in the present invention, a method disclosed in Patent Document 8can be used. That is, the production method of an active silicic acidaqueous solution by hydrolysis of tetraalkoxysilane with acid catalystin a composition of 1 to 8 mol/L tetrametoxysilane, 0.0018 to 0.18 mol/Lacid, and 2 to 30 mol/L water without using solvent, then diluting withwater so as to adjust the silica concentration within range of 0.2 to1.5 mol/L.

A production method of colloidal silica of the present invention can beillustrated as follows. First, an active silicic acid aqueous solutionis produced as mentioned above. Said basic nitrogen compounds are addedto the said active silicic acid aqueous solution so as to alkalize thesolution. Then, colloidal particles are formed by heating the solution(a seed particles forming process, process (b-1) of claim 9). Next,above mentioned active silicic acid aqueous solution and an alkalizingagent or above mentioned active silicic acid aqueous solution, the basicnitrogen compounds, and the alkalizing agent are added to the colloidalsolution formed in the previous process while maintaining in alkalinecondition under heating condition to grow colloidal solution (aparticles growing process, process (b-2) of claim 9). At the seedparticles forming process, the basic nitrogen compounds are usedtogether with the alkalizing agent, however, at the particles growingprocess, use of the alkalizing agent alone is possible.

Specifically, in above mentioned seed particles forming process andparticles growing process, conventional operations are used. Forexample, seed particles whose short axis length (thickness) is of 5 to20 nm can be formed as follows. First, silica concentration of an activesilicic acid aqueous solution is set to 2 to 7 wt %. By adding basicnitrogen compounds, a pH of the solution is adjusted to 8 to 11. Thesolution is heated to the temperature of 60 to 240° C. to obtain saidseed particles. Said seed particles can be grown to silica particleswhose short axis length (thickness) is of 10 to 150 nm using a build upmethod. That is, the method of adding an active silicic acid aqueoussolution and an alkalizing agent or the active silicic acid aqueoussolution, basic nitrogen compounds, and the alkalizing agent to thecolloidal solution of said seed particles whose pH is of 8 to 11 andtemperature is of 60 to 240° C. The process is carried out whilemaintaining the solution at the pH of 8 to 11.

Above mentioned production method is almost same as a conventionalproduction method that uses alkali metal hydroxide or alkali silicate asan alkalizing agent. However, at a point that using an active silicicacid aqueous solution obtained by hydrolysis of tetraalkoxysilaneinstead of an active silicic acid aqueous solution made from sodiumsilicate, at a point that using basic nitrogen compounds instead ofalkali metal hydroxide in a seed particles forming process, and at apoint that using an organic alkalizing agent or the basic nitrogencompounds and the organic alkalizing agent instead of alkali metalhydroxide in particles growing process, the production method of thepresent invention is different from the conventional production method.

As the alkalizing compound used in the particles growing process,quaternary ammonium hydroxide is desirably used, in particular,tetramethylammonium hydroxide, tetraethylammonium hydroxide or cholinehydroxide are more desirable. Said organic alkalizing agent is preferrednot to contain alkali metals.

As a tetraalkoxysilane used in the present invention,tetramethoxysilane, tetraethoxysilane or the like can be mentioned,however, silicic acid oligomer whose degree of polymerization of 2 to 10and which is on the market (for example, “Ethylsilicate 40”, product ofColcoat Co., Ltd.) can also be used. In a case of usingtetraalkoxysilane, use of a high purified product is desirable.

As the next process, concentration of silica by ultra-filtration iscarried out. Concentration by water evaporation can also be used,however, ultra-filtration is more advantageous from the view point ofenergy consumption.

An ultra-filtration membrane to be used at the concentration process ofsilica by ultra-filtration can be illustrated as follows. Separationwhich uses the ultra-filtration membrane is objecting particles withsize of 1 nm to several microns. Since dissolved polymer product is alsobeing objected, filtration accuracy is indicated by molecular cutoff innano-meter region. In the present invention, an ultra-filtrationmembrane whose molecular cutoff value is smaller than 15000 is desirablyused. By using the ultra-filtration membrane of said range, particleslarger than 1 nm can be separated. More desirably, an ultra-filtrationmembrane whose molecular cutoff value is 3000 to 15000 is used. Whenultra-filtration membrane whose molecular cutoff value is smaller than3000 is used, filtration resistance becomes too high and disadvantageousfrom economical view point, and when molecular cutoff value is over15000, purification accuracy is deteriorated. As a material of amembrane, polysulfone, polyacrylonitrile, sintered metal, ceramics,carbon or the like can be used, however, from the view point of heatresistance and filtration speed, a membrane made from polysulfone ispreferable and easier to use. As a shape of the membrane, any kinds ofshapes, such as spiral shape, tubeler shape, hollow filament shape orthe like can be used. However, among said shapes, hollow filament shapeis preferable because it is compact and easier to use. Further, when theultra-filtration process acts concurrently as washing and removingprocess of excess basic nitrogen compounds, it is possible to improveremoving rate by adding pure water even after reaching the aimedconcentration. Furthermore, it is also desirable to remove strong acidanion which added as a catalyst of hydrolysis. It is desirable toconcentrate silica so as the concentration of silica to be of 10 to 50wt %.

Further, before or after an ultra-filtration process, a purificationprocess by ion-exchange resin can be added if necessary. For example,above mentioned strong acid anion can be removed by contacting with OHtype strong basic anion-exchange resin.

Basic nitrogen compounds dissolved in water phase diminish together withwater at concentration process by ultra-filtration. When the amount ofbasic nitrogen compounds became too small, it is desirable to supply thecompound after concentration process.

However, existence of an organic compound may cause secondary problem ina liquid-waste treatment process. Considering such a case, a productfrom which basic nitrogen compounds is removed is also required. Amethod of reducing the amount of the basic nitrogen compounds aspossible by using ultra-filtration effectively is involved in thepresent invention as one of the production method.

Colloidal silica forming nonspherical particles cluster is characterizedto have a shape similar to a caterpillar or a bended rod. Each particlehas a different shape, and specifically, said colloidal silica containssilica particles having a shape shown in FIGS. 1 to 4. Long axis/shortaxis ratio of the colloidal silica is within the range of 1.2 to 20. Themost part of the particles are not extended straightly, and nonextendedparticles are partially existed. Only a few silica particles are shownin FIGS. 1 to 4 as examples, although shapes are changeable by producingconditions, nonspherical shaped ones are major.

Average long axis/short axis ratio of silica particles of the colloidalsilica for polishing of the present invention is within the range of 3to 15 which is suited as polishing particles. If the ratio is largerthan 15, the particles intertwine with each other, and if the ratio issmaller than 3, the polishing speed drops.

In a polishing process, a shape of silica particles is a very importantfactor. That is, by a corrosive action of alkaline, a thin eroded layeris formed on a surface of an object to be polished, and removal rate ofthe thin layer is changed largely by the shape of particles. When thesize of silica particles becomes larger, the removal rate increases.However, scratches are formed easily on the polished surface. Also,nonspherical particles promises larger removal rate compare to sphericalshaped particles, however, scratches are formed easily on the polishedsurface. Therefore, it is desirable that the particles have an adequatesize and shape, and the particles must not be crushed easily oragglomerate to form gel.

A shape of the silica particles of the colloidal silica for polishing ofthe present invention is very similar to the shape of fumed silica.Silica particles of fumed silica generally form nonspherical elongatedparticles cluster whose long axis/short axis ratio is of 5 to 15.Primary particle size of fumed silica (can be simply described asparticle size) indicates short axis length (thickness) and is normally 7to 40 nm. Further, these particles agglomerate and form secondaryparticles and appearance of slurry is white. Therefore, when the slurryof fumed silica is preserved for long time, particles tend toprecipitate and cause scratches on the polished surface.

On the contrary, although silica particles of the present invention havesimilar shape to primary particles of fumed silica, silica particles donot form secondary particles by agglomeration, and appearance of slurryis transparent or semi-transparent. Particles do not have tendency toprecipitate and do not cause scratches on the polished surface.

Desirable average short axis length of silica particles of the colloidalsilica for polishing composed of silica particles of the presentinvention is of 5 to 30 nm by an electric micrometer observation, andconcentration of silica particles is of 2 to 50 wt %. When average shortaxis length of silica particles is smaller than 5 nm, polishing rate islow and stability of colloid is lacked because particles easilyagglomerate. Further, when average short axis length is larger than 30nm, scratches are easily caused and flatness of the polished surfacedeteriorates.

The present invention can provide a polishing compound that containingabove mentioned colloidal silica for polishing and further, componentsthat can further improve polishing ability are added.

In the present invention, polishing rate can be remarkably improved byelevating the electric conductivity value of the polishing compoundsolution. Electric conductivity is an index value of conduction ofelectricity, and indicated by a reciprocal number of electric resistanceper unit length. In the present invention, electric conductivity isindicated as converted number of electric conductivity (milli Siemens)to 1 wt % of silica. In. the present invention, when electricconductivity at 25° C. is larger than 15 mS/m/1%-SiO₂, it is desirableto improve the polishing rate and larger than 20 mS/m/1%-SiO₂ is moredesirable. Since addition of salts deteriorates stability of colloid,upper limit for amount of salts addition does exist. Upper limit ischangeable according to particle size of silica, however, isapproximately 60 ms/m/1%- SiO₂.

As a method to elevate an electric conductivity, following two methodscan be mentioned. One is to elevate concentration of a buffer solutionand another is to add salts. To elevate concentration of the buffersolution, one can elevate only concentration of basic nitrogen compoundsand strong acid without changing a molar ratio. Or, one can elevate onlyconcentration of weak acid and quaternary ammonium hydroxide withoutchanging a molar ratio. Salts used for the method of adding salts arecomposed of acid and base mixture, and as an acid, both strong and weakacid can be used. Mineral acid, organic acid or mixture of these acidscan also be used. As a base, use of water soluble quaternary ammoniumhydroxide is desirable, because it is not desirable to increase theamount of alkali metal hydroxide.

As a salt composed by strong acid and quaternary ammonium base, it isdesirable to use at least one of the compounds selected from the groupconsisting of quaternary ammonium sulfate, quaternary ammonium nitrate,and quaternary ammonium fluoride. As a cationic ion composing quaternaryammonium strong base, choline ion, tetramethylammonium ion ortetraethylammonium ion are desirable.

A polishing compound containing colloidal silica for polishing of thepresent invention is desirable to contain a chelating agent that forms awater insoluble chelate compound with copper. For example, as saidchelating agent, public known compounds like azoles, such asbenzotriazole, or quinoline derivatives, such as quinolinol orquinaldine acid, are desirably used.

For the purpose of improving the feature of said colloidal silica forpolishing, surfactant, a water soluble polymer compound or a deformingagent can be used together with.

As a surfactant, nonionic surfactant is desirably used. Nonionicsurfactant has a function to protect excess etching. For example,polyoxyalkylenealkylether, such as polyoxyethylenelaurylether, fattyacid ester, such as glycerinester, or polyoxyalkylenealkylamine, such asdi(polyoxyethylene)laurylamine, can be used. Preferable concentration ofnonionic surfactant contained in a polishing compound containingcolloidal silica for polishing is of 0.001 to 0.1 wt %.

As a water soluble polymer compound, at least one of the compoundsselected from the group consisting of hydroxyethyl cellulose,polyethylene glycol or polyvinylalcohol is desirable. These compoundshave a protecting effect for excess etching.Ethyleneoxide-propyleneoxideblock copolymer is also desirably used. Forexample, when hydroxyethyl cellulose is used, it acts as a water solublepolymer in the concentration range of 30 to 300 ppm when it is added tothe 1 to 100 diluted polishing compound. Therefore, requiredconcentration of hydroxyethyl cellulose in an original polishingcompound is of 0.3 to 3 wt %. In the same way, in a case ofpolyethyleneglycol, required concentration is of 0.3 to 5 wt %, and in acase of polyvinylalcohol, required concentration is of 0.1 to 5 wt %.

As a defoaming agent, silicone emulsion is desirably used. As siliconeemulsion, silicone defoaming agent being on the market, which is O/Wtype emulsion of silicone oil mainly composed of polydimethylsiloxanecan be used. Concentration of defoaming agent in polishing compound isof 0.01 to 0.1 wt %.

A polishing compound containing colloidal silica for polishing of thepresent invention is said as an aqueous solution, however, an organicsolvent can be added. Other abrasives, such as colloidal alumina,colloidal ceria or colloidal zirconia, bases, additives or water can bemixed with said polishing compound of the previous invention during aproducing process.

Regarding the polishing compound containing colloidal silica forpolishing of the present invention, it is desirable to produce withsilica concentration of 20 to 50 wt %, and dilution is carried out withpure water at actual use. A pH adjusting agent or salts for adjusting anelectric conductivity is added if it is required.

EXAMPLES

The present invention will be illustrated in more detail in examples. Inexamples, following equipments are used.

(1) TEM observation: Transmission Electron Microscope H-7500 of HitachiLtd., is used.

(2) Specific surface area by BET method: Flow Sorb 2300 of ShimadzuCorporation is used.

(3) Analysis of basic nitrogen compounds except hydrazine: Total organiccarbon meter TOC-5000A, SSM-5000A of Shimadzu Corporation is used.Carbon amount is converted into basic nitrogen compounds. Specifically,total organic carbon amount (TOC) is calculated by numerical formula ofTOC=TC-IC after total carbon amount (TC) and inorganic carbon amount(IC) are measured. As a standard for TC measurement, a glucose aqueoussolution of 1 wt % carbon amount is used, and as a standard for ICmeasurement, sodium carbonate of 1 wt % carbon amount is used. Ultrapurewater is used as a standard of 0 wt % carbon amount. By using abovementioned standards, calculation curves of 150 μL and 300 μL for TC andof 250 μL for IC are prepared. At TC measurement, 100 mg of specimen ispicked and burned in a combustion furnace of 900° C. And at ICmeasurement, 20 mg of specimen is picked, and about 10 mL of (1+1)phosphoric acid are added. The reaction is accelerated in a combustionfurnace of 200° C.

(4) Analysis of hydrazine: Absorptiometer UV-VISIBLE RECORDING SPECTROPHOTOMETER UV-160 of Shimadzu Corporation is used. Measurement iscarried out according to p-dimethylbenzaldehyde absorption methodregulated in JIS B8224. Specifically, specimen is acidized byhydrochloric acid, followed by addition of p-dimethylbenzaldehyde, toobtain a yellowish compound. Absorbancy of the yellowish compound ismeasured and hydrazinium ion is quantitated. From the obtained value ofhydrazinium ion, concentration of hydrazine is calculated.

(5) Analysis of tetramethylammonium hydroxide (TMAOH): Ion ChromateICS-1500 of Dionex Corporation is used. Specifically, in cases of liquidphase TMAOH, specimen is diluted 1000 to 5000 times with pure water andmeasured. Further, in cases of total TMAOH, as a previous treatment, 3 gof 20 wt % NaOH and pure water are added to 5 g of specimen, heated to80° C. and silica is perfectly dissolved. Obtained dissolved solution isdiluted 1000 to 5000 times with pure water and total TMAOH amount ismeasured.

(6) Analysis of metal elements: ICP emission spectrometry ULTIMA 2 ofHoriba, Ltd. is used.

Example 1

Hydrolysis of tetrametoxysilane is practiced by a composition of 4.49mol/L tetrametoxysilane, 0.01 mol/L acid, and 18.38 mol/L water withoutusing solvent. Practically, hydrolysis is performed by processesmentioned below.

Diluted hydrochloric acid solution is prepared by adding 0.2 g of 35%hydrochloric acid into 46 g of deionized water. 96 g oftetrametoxysilane (special grade reagent, converted SiO₂ concentrationis 39 wt %) is placed into a container, then above mentioned dilutedhydrochloric acid solution is added with stirring. At the first stage,said two solutions are separated and are not mixed well. After severalminutes, hydrolysis reaction starts with heat evolution, and the mixturebecomes transparent homogeneous solution. Stirring is continued another30 minutes so as the hydrolysis reaction to be completed, and hydrolyzedsolution is obtained. Then said solution is diluted by adding 116 g ofdeionized water to prevent the polymerization of active silicic acid.742 g of deionized water is poured into another container. The abovementioned hydrolyzed solution is added and total amount is brought up to1000 g. The solution is matured by stirring for 16 hours. Thus, anactive silicic acid aqueous solution having SiO₂ concentration of 3.7 wt% (approximately 0.6 mol/L) and a pH of 2.6 is obtained.

An aqueous solution of basic nitrogen compounds is prepared by a methodmentioned below. Ethylenediamine anhydride is dissolved in deionizedwater and a 10 wt % aqueous solution is prepared. Crystal ofdiethylenediamine(piperazine)-6- hydrate is dissolved in deionized waterand a 8 wt % aqueous solution is prepared. Crystal of imidazole isdissolved in deionized water and a 10 wt % aqueous solution is prepared.Crystal of 2-methylimidazole is dissolved in deionized water and a 10 wt% aqueous solution is prepared. A piperidine solution is diluted withdeionized water and a 10 wt % aqueous solution is prepared. A morpholinesolution is diluted with deionized water and a 10 wt % aqueous solutionis prepared. Crystal of L(+)-arginine is dissolved in deionized waterand a 10 wt % aqueous solution is prepared. A hydrazine 1-hydratesolution is diluted with deionized water and a 5 wt % aqueous solutionis prepared. Reagents are used for all of above mentioned basic nitrogencompounds.

As quaternary ammonium hydroxide, a 25% tetramethylammonium hydroxideaqueous solution on the market and a 35% tetraethylammonium hydroxideaqueous solution on the market are used without dilution.

An aqueous solution of basic nitrogen compounds prepared as above areadded by the amount mentioned in Table 1 to 50 g of an active silicicacid aqueous solution whose silica concentration is 3.7 wt % and a pH is2.6 at 25° C. Measured pH values are summarized in Table 1. After that,solutions are heated with stirring, and maintained at 100° C. for 1 hourto form colloid particles. Solutions are cooled down to 25° C. and a pHis measured. Measured pH values are summarized in Table 1. According tothe observation by a transmission electron microscope (TEM), shapes ofany kinds of obtained colloidal silica are similar regardless of kind ofbasic nitrogen compounds, and colloidal particles form irregularlyconnected nonspherical particles cluster characterizing that short axislength of about 6 to 7 nm, long axis/short axis ratio of 5 to 20, andaverage long axis/short axis ratio of 10 to 15. As a typical example,TEM picture of colloidal silica prepared using diethylenediamine isshown in FIG. 1.

TABLE 1 colloidal silica added pH average amount after short basicnitrogen compound (g) added pH axis (nm) 10% ethylenediamine 1.6 8.510.0 7-30  8% diethylenediamine 3.0 8.5 9.8 ≈7 10% imidazole and 4.5 and9.0 9.5 ≈7 35% tetraethylammonium hydroxide 1.0 10% methylimidazole 6.78.7 9.2 ≈5 10% piperidine 2.0 8.2 8.9 ≈5 10% morpholine 7.0 8.9 9.7 7-1010% arginine 5.0 8.3 9.5 ≈7  5% hydrazine 4.0 7.9 8.7 ≈5

Example 2

By same method as Example 1, tetramethoxysilane is hydrolyzed and anactive silicic acid aqueous solution having SiO₂ concentration of 3.7 wt% and a pH of 2.6 is obtained. The pH is adjusted to 9.8 by adding 64 gof a 10% morpholine aqueous solution to 500 g of the active silicic acidaqueous solution with stirring. After that, solutions are heated withstirring, maintained at 100° C. for 1 hour, to form colloid particles.Then, while maintaining the temperature at 100° C., 2600 g of the activesilicic acid aqueous solution and 40 g of the 10% morpholine aqueoussolution are simultaneously added by 4 hours to grow silica particles.After adding process, the solution is matured by maintaining thetemperature at 100° C. for 1 hour, then cooled down.

Silica concentration of obtained colloidal silica becomes 5.6 wt % dueto evaporation of water and a pH at 25° C is 9.0. According to atransmission electron microscope (TEM) observation, obtained colloidalsilica is composed of colloidal particles forming irregularly connectednonspherical particles cluster characterized that short axis length ofabout 18 nm, long axis/short axis ratio of 1.2 to 7, and average longaxis/short axis ratio of 3. TEM picture is shown in FIG. 2. Particlesize calculated from BET method specific surface area is 16 nm.

Example 3

Colloidal silica obtained by Example 2 is concentrated. After that,pressure filtration by pump circulation is carried out using hollowfiber ultra-filter membrane whose molecular cutoff value is 6000(MICROZA UF MODULE SIP-1013, product of ASAHI KASEI Corp.). In this way,colloidal silica is concentrated to make the solution having SiO₂concentration of 22.1 wt % and approximately 520 g of concentratedcolloidal silica is obtained. Obtained colloidal silica has a pH of 8.6at 25° C., and alkali metal concentration is smaller than 1 ppm.

Example 4

100 g of colloidal silica obtained in Example 3 is placed into acontainer. To this colloidal silica, 10 g of a 10% morpholine aqueoussolution is added and a pH of 9.5 is measured. Then the pH is adjustedto 9.0 by adding 5 g of 2.0 wt % hydrochloric acid. When said colloidalsilica is diluted 10 times with deionized water, the pH is measured as9.1 and when said colloidal silica is diluted 100 times, the pH ismeasured as 9.2. That is, by mixing morpholine and hydrochloric acid, pHbuffer solution against dilution is formed.

Example 5

Hydrolysis of tetrametoxysilane is practiced by composition of 3.38mol/L tetrametoxysilane, 0.01 mol/L acid, and 13.81 mol/L water withoutusing solvent. Practically, hydrolysis is performed by processesmentioned below.

A diluted hydrochloric acid solution is prepared by adding 1 g of 35%hydrochloric acid into 100 g of deionized water. 96 g oftetraetoxysilane (special grade reagent, converted SiO₂ concentration is29 wt %) is placed into a container, then above mentioned dilutedhydrochloric acid solution is added with stirring. At the first stage,said two solutions are separated and are not mixed well. After severalminutes, hydrolysis reaction starts with heat evolution, and the mixturebecomes transparent homogeneous solution. Stirring is continued another30 minutes so as the hydrolysis reaction to be completed, and hydrolyzedsolution is obtained. Then said solution is diluted by adding 100 g ofdeionized water to prevent the polymerization of active silicic acid.590 g of deionized water is poured into another container. The abovementioned hydrolyzed solution is added and total amount is brought up to835 g. The solution is matured by stirring for 16 hours. Thus, an activesilicic acid aqueous solution having SiO₂ concentration of 3.7 wt %(approximately 0.6 mol/L) and a pH of 2.5 is obtained.

By same method as Example 1, a 8 wt % diethylenediamine aqueoussolution, a 10 wt % piperidine aqueous solution, a 10 wt % morpholineaqueous solution, a 10 wt % arginine aqueous solution and a 10 wt %hydrazine aqueous solution are prepared.

As quaternary ammonium hydroxide, a 25% tetramethylammonium hydroxideaqueous solution on the market and a 35% tetraethylammonium hydroxideaqueous solution on the market. are used without dilution.

An aqueous solution of basic nitrogen compounds prepared as above areadded by the amount mentioned in Table 2 to 250 g of aqueous solution ofactive silicic acid whose silica concentration is 3.7 wt % and a pH is2.5, then pH is measured at 25° C. Measured pH values are summarized inTable 2. After that, solutions are heated with stirring and maintainedat 100° C. for 1 hour to form colloid particles. Solutions are cooleddown to 25° C. and a pH is measured. Measured pH values are summarizedin Table 2. According to the observation by a transmission electronmicroscope (TEM), shapes of all kinds of obtained colloidal silica aresimilar regardless of kind of basic nitrogen compounds. Obtainedcolloidal particles form irregularly connected nonspherical particlescluster characterizing that short axis length of about 5 to 7 nm, longaxis/short axis ratio of 5 to 20, and average long axis/short axis ratioof 10 to 15. As a typical example, TEM picture of colloidal silicaprepared using morpholine is shown in FIG. 3.

TABLE 2 colloidal silica added pH average amount after short basicnitrogen compound (g) added pH axis (nm)  8% diethylenediamine 15.4 8.69.8 5.5 10% piperidine 10.4 8.6 8.9 ≈5 10% morpholine 18.2 8.6 9.1 4.810% arginine 21.3 8.6 9.5 5.4 10% hydrazine 10.5 8.5 9.0 5.3

Example 6

By same method as Example 5, tetraethoxysilane is hydrolyzed and anactive silicic acid aqueous solution having SiO₂ concentration of 3.7 wt% and a pH of 2.5 is obtained. And, a 2.5 wt % morpholine aqueoussolution is also prepared by diluting a 10 wt % solution. The pH isadjusted to 8.6 by adding 18 g of the 10% morpholine aqueous solution to250 g of the active silicic acid aqueous solution with stirring. Afterthat, solutions is heated with stirring and maintained at 100° C. for 1hour to form colloid particles. Then, while maintaining the temperatureat 100° C., 1600 g of the active silicic acid aqueous solution and 420 gof 2.5 wt % morpholine aqueous solution are simultaneously added by 4hours to grow silica particles. After adding process, the solution ismatured by maintaining the temperature at 100° C. for 1 hour, thencooled down.

The pH of obtained colloidal silica is 9.7 at 25° C. According to atransmission electron microscope (TEM) observation, obtained colloidalsilica is composed of colloidal particles forming irregularly connectednonspherical particles cluster characterized that short axis length ofabout 18 nm, long axis/short axis ratio of 1.2 to 7, and average longaxis/short axis ratio of 3. TEM picture is shown in FIG. 4. Particlesize calculated from BET method specific surface area is 13 nm.

Example 7

Colloidal silica obtained in Example 7 is concentrated. Pressurefiltration by pump circulation is carried out using hollow fiberultra-filter membrane whose molecular cutoff value is 6000 (MICROZA UFMODULE SIP-1013, product of ASAHI KASEI Corp.). In this way, colloidalsilica is concentrated to the silica concentration 11.8 wt % andapproximately 460 g of concentrated colloidal silica is obtained.Obtained colloidal silica has a pH of 9.3 at 25° C., and alkali metalconcentration is smaller than 1 ppm.

Example 8

By same method as Example 5, tetraethoxysilane is hydrolyzed and anactive silicic acid aqueous solution having SiO₂ concentration of 3.7 wt% and a pH of 2.5 is obtained. The pH is adjusted to 8.6 by adding 21 gof a 10% arginine aqueous solution to 250 g of the active silicic acidaqueous solution with stirring. After that, solutions are heated withstirring, maintained at 100° C. for 1 hour to form colloid particles.Then, while maintaining the temperature at 100° C., 1400 g of the activesilicic acid aqueous solution and 400 g of a 2.7 wt % arginine aqueoussolution are simultaneously added by 4 hours to grow silica particles.The 2.7 wt % arginine aqueous solution is prepared by diluting a 10 wt %arginine aqueous solution. After adding process, the solution is maturedby maintaining the temperature at 100° C. for 1 hour, then cooled down.

The pH of obtained colloidal silica is 9.8 at 25° C. According to atransmission electron microscope (TEM) observation, obtained colloidalsilica is composed of colloidal particles forming irregularly connectednonspherical particles cluster characterized that short axis length ofabout 18 nm, long axis/short axis ratio of 1.2 to 7, and average longaxis/short axis ratio of 3. Particle size calculated from BET methodspecific surface area is 11 nm.

Example 9

Colloidal silica obtained by Example 8 is concentrated. Pressurefiltration by pump circulation is carried out using hollow fiberultra-filter membrane whose molecular cutoff value is 6000 (MICROZA UFMODULE SIP-1013, product of ASAHI KASEI Corp.). In this way, thecolloidal silica is concentrated to SiO₂ concentration of 8.3 wt %, andapproximately 510 g of concentrated colloidal silica is obtained.Obtained colloidal silica has a pH of 9.6 at 25° C., and alkali metalconcentration is smaller than 1 ppm.

1. A colloidal silica for semiconductor wafer polishing comprising,colloidal silica prepared from an active silicic acid aqueous solutionobtained by hydrolysis of tetraalkoxysilane and at least one nitrogencontaining basic compound selected from a group consisting ofethylenediamine, diethylenediamine, imidazole, methylimidazole,piperidine, morpholine, arginine and hydrazine, wherein said colloidalsilica contains nonspherical silica particles and pH of the colloidalsilica is of 8.5 to 11.0 at 25° C.
 2. The colloidal silica forsemiconductor wafer polishing of claim 1 further comprising,tetramethylammonium hydroxide, tetraethyl ammonium hydroxide or cholinehydroxide.
 3. The colloidal silica for semiconductor wafer polishing ofclaim 1 further comprising, a buffer solution composed of mixing basicnitrogen compounds and strong acid or of mixing weak acid and quaternaryammonium hydroxide, wherein said colloidal silica for semiconductorwafer polishing displays pH buffering action in the pH range of 8.5 to11.0 at 25° C.
 4. The colloidal silica for semiconductor wafer polishingof claim 2 further comprising, a buffer solution composed of mixingbasic nitrogen compounds and strong acid or of mixing weak acid andquaternary ammonium hydroxide, wherein said colloidal silica forsemiconductor wafer polishing displays pH buffering action in the pHrange of 8.5 to 11.0 at 25° C.
 5. The colloidal silica for semiconductorwafer polishing of claim 1, wherein said tetraalkoxysilane istetramethoxysilane or tetraethoxysilane.
 6. The colloidal silica forsemiconductor wafer polishing of claim 1, wherein average short axislength of said silica particles is of 5 to 30 nm, long axis/short axisratio is of 1.2 to 20, and average long axis/short axis ratio is of 3 to15.
 7. The colloidal silica for semiconductor wafer polishing of claim1, wherein said colloidal silica is an aqueous solution whoseconcentration of silica to entire colloidal silica solution is of 2 to50 wt %.
 8. The colloidal silica for semiconductor wafer polishing ofclaim 1, wherein said colloidal silica is an aqueous solution whoseconcentration of alkali metal to entire colloidal silica solution isless than 1 ppm.
 9. A production method of colloidal silica forsemiconductor wafer polishing of claim 1 comprising: (a) a producingprocess of an active silicic acid aqueous solution by hydrolysis oftetraalkoxysilane with acid catalyst in a composition of 1 to 8 mol/Lsilica, 0.0018 to 0.18 mol/L acid, and 2 to 30 mol/L water without usingsolvent, then diluting with water so as to adjust the silicaconcentration within range of 0.2 to 1.5 mol/L; and (b-1) a formationprocess of colloidal particles by heating said active silicic acidaqueous solution after alkalizing the solution by adding said basicnitrogen compounds; and (b-2) a growing process of colloidal particlesby adding said active silicic acid aqueous solution and an alkalizingagent or said active silicic acid aqueous solution, said basic nitrogencompounds, and the alkalizing agent to colloidal particles formed in theprocess (b-1) while maintaining in alkaline condition under heatingcondition.
 10. The production method of colloidal silica forsemiconductor wafer polishing of claim 9 further comprising, (c) aconcentration process of the colloidal silica after the process (b-2).